In this project which was designed to study the history of changes in the concept of fever from the eighteenth to the twentieth centuries, as we are tracing the successive definition of the various diseases, all of which were once considered to be simply fever. Physicians' ideas of the nature of fever were influenced deeply by the particular fevers that they encounterd in practice. Thus the concepts of fever held by physicians might vary as a result of variations in the geographical distribution of disease, or as a result of differences in living conditions among different social classes, or between the urban and rural communities. Physicians' experience of disease also often reflected movements of people brought about by such factors as emigration, trade, industrialization, war, enslavement, or famine. Fevers were the prevailing diseases of the eighteenth and nineteenth centuries, and because of the vast prevalence of fevers the history of concepts of fever over those 200 years is a history of evolution of scientific concepts of disease within medicine.